This invention relates to a temperature-actuated mixing valve of the general type used to control in-line water temperature in potable hot water systems. Such valves are typically used at the hot water source, such as at a gas or electric hot water heater or boiler. The temperature of the water allowed to flow downstream from the mixing valve is maintained within a predetermined range of temperature by mixing hot and cold water entering the valve on the upstream end. The invention is therefore described with reference to such a hot water system. However, principles of the invention also have application with other liquids and with gases, and for this reason the application is intended to encompass both liquids and gases, and liquids other than water.
Most prior art mixing valves utilize a thermal actuator, which acts as the "motor" of the valve. Such actuators convert thermal energy into mechanical movement. The operating principle of most such devices is based upon the large increase in volume of a thermosensitive material such as wax which, when heated, changes from a solid to a liquid. When such a thermosensitive material is enclosed within a confined space, heating causes the material to expand against a piston to perform work. In some cases such actuators are either provided with two oppositely-acting pistons to increase the range of motion, or two such actuators are placed end-to-end to accomplish the same function. By incorporating a thermal actuator into a mixing valve, hot and cold supply pressures and temperatures can be regulated.
A common problem in the use of such devices is that if the shuttle has moved as far as it can move within the valve, but the piston of the thermal actuator is still trying to move, there must be some means of consuming this extra travel. Otherwise the valve can be damaged or destroyed. This is most often accomplished in the prior art by the use of an overtravel spring mounted around an adjusting bolt in the top of the valve. This solution creates several additional problems. First, this arrangement adds height to the mixing valve, which may prevent or restrict use in confined areas, or promote breakage under impact. Second, the overtravel spring must be preloaded, requiring a means for retaining the spring on the adjusting bolt. Finally, in applications where two thermal actuators are used back-to-back, there must be some way to retain both elements in the shuttle.
In addition, mixing valves are often difficult to disassemble for repair or maintenance, and require the use of tools, often in confined spaces.
The design features of the present invention solve the known prior art problems simply and efficiently.